By that time the fortified town was essentially a large wet dock, a harbor were the tide was kept out by a lock door.

In the late eighteenth century the Dutch had also been unable to ascertain a steady supply of good Scandinavean oak for ships.

Both circumstances made that by 1795, the traditional method of maintaining warships by careening them, was no longer effective.

What was needed was a dry dock, where warships could be cleaned regularly and easily without damaging them.

At the time, the Dutch had Vlissingen Navy Drydock, but since 1746 this had been out of order due to technical problems.

In 1796, Jan Blanken published a work about the construction of dry docks in Holland, and especially in Hellevoetsluis.

[3] As an alternative, he proposed that a lock could be used to lift even the heaviest ships to the ebb level, and to construct the dry dock at that height.

In 1798–1799, the sea lock was widened from 50 to 54 feet, so the latest heavy ships were again able to enter the wet dock.

[11] In August 1812 there was a tender for the final completion of the construction dock inrigting van aanbouw.

In about 1880, the dimensions of the dry dock were given as 71 m long, with an entrance at Amsterdam Ordnance Datum water level of 15.90 m wide.

If water was 0.1 m above AOD, the caisson door could be opened, and a ship with a draft of 4.45 m could enter the dock.

[15] Therefore, about 0.7 m would have to be added again to the 3.7 m to get a regular draft of 4.4 m for ships willing to enter the dry dock at high tide.

On 17 April 1806 a like ship door was launched in Hellevoetsluis, and placed to close the dry dock.

[19] The docking was delayed for a day by trouble with the steam engine, but by early morning on 16 September she was out again.

[21] Later in 1811 Jan Blanken got the assignment to build a large naval base near Nieuwediep, Den Helder, later called Willemsoord It would include another dry dock.

For about 50 years after it was opened, Hellevoetsluis Dry Dock could meet almost any demand of the Dutch navy.

[22] In May 1867 Willemsoord Dry Dock II was finally finished, but at horrendous cost.

The fact that the old dry dock in Vlissingen had by then also become too small for the latest ships might have played its part.

After the navy left Hellevoetsluis, the dry dock was exploited by a private industry.

Most of the time these are small historic ships that contribute to the experience of tourists visiting Hellevoetsluis.